The invention relates generally to bipolar pulse generators. More specifically, the invention relates to bipolar pulse generators that incorporate voltage multiplication (transformation) circuitry and time separation between positive and negative sub-pulses.
Recent development trends in pulse power microwave sources for a variety of applications have been directed to increasing power and efficiency as well as energy density (energy per volume). Transmission line type pulse generators with different kinds of fast switches, including light activated photoconductive switches, can achieve some of the best results. In particular, such transmission line type pulse generators are compact and provide a very fast pulse rise time and a very high power.
For a given limited charging voltage of transmission lines defined by high-current switches, high powered and high energy density transmission lines imply low characteristic impedances. The low range of characteristic impedances frequently causes problems for coupling with typically load impedances, for example 50 Ohm or higher, or radiating impedances, which introduces a problem with high ratio impedance transformation.
There are many different applications of bipolar pulse generators, for example, in industry, physics and medicine. Very often bipolar pulse generators with time separation between positive and negative sub-pulses are preferable or required. Bipolar pulse generators capable of separation between positive and negative sub-pulses are certainly known. Examples of such pulse generators are disclosed in “Design of Bipolar Pulse Generator for Ferroelectric Electron Emission Extraction”, Feng Chen et al., Pulsed Power IEE Symposium, 2000, U.S. Pat. No. 6,214,297 issued to Zhang et al. entitled “High Voltage Pulse Generator”, and SU Patent 1 254 994 A1 issued to Remnev G. E. et al. in 1994 entitled “Powerful Generator of Twin Pulses”, the content of each of which is incorporated herein by reference.
There are, however, disadvantages associated with the above-referenced bipolar pulse generators. For example, all of the above-referenced generators do not provide voltage (impedance) transformation without an additional pulse transformer. In addition, the conventional pulse generators are general complex in nature, require more than one switch, and can be difficult to implement in real world applications, especially for high power applications. Still further, the switching elements required in U.S. Pat. No. 6,214,297 and SU Patent 1 254 994 A1 require very short (sub-nanosecond range) rise times, which are almost impossible to realize.
The present applicant has previously developed an efficient transmission line based pulse generator, which is described in US Patent Application 2007/165,839 entitled “Bipolar Pulse Generators with Voltage Multiplication”, the content of which is incorporated herein by reference, which provides all required voltage/impedance transformation and high power pulses with a single switch. Any type of switch can be used in described pulse generator, including those in which it is necessary to generate nanosecond range pulses. Further, because only a single switch is utilized, there are no problems associated with switching time synchronization. The bipolar pulse generators in the above-referenced patent application, however, do not have any gap between positive and negative sub-pulses.
In all cases, energy stored in a voltage charged transmission line is proportional to the reverse value of line's characteristic impedance. In order to make a comparison of different generator's circuits, the total energy stored in all equally voltage charged transmission lines could be related to the energy stored in a transmission line with critical (minimum) characteristic impedance as a reference. The lower characteristic impedance implies the lower space between line's conductors and the higher electric field, which is a limitation for selected voltage defined by switch.
Accordingly, there remains a need for a bipolar pulse generator solution based on voltage charged transmission lines which provides separation between positive and negative sub-pulses, as well as a need for a bipolar pulse generator with pulse separation that provides high pulse power, and that also provides high voltage/impedance transformation.
In view of the above, it would be desirable to provide a bipolar pulse generator that can address the needs set forth above, that can be implemented in a simple transmission line structure with a single switch, which has a relatively small total size, and that allows simple access by fibers to a closing photoconductive switch(s) that actuates the bipolar pulse generator.